Defects inspection through detection of magnetic fields

Abstract

Various embodiments include apparatus and methods to inspect casing defects in a pipe such as a casing associated with a drilling operation. Electrical connectors contacting the inside wall of the pipe can be used to generate a current in the pipe. Magnetic fields correlated to an anomaly or anomalies that alter the current can be sensed to identify the presence of the anomaly or anomalies. Additional apparatus, systems, and methods are disclosed.

What is claimed is: 
     
       1. An apparatus comprising:
 two electric connectors coupled to an alternating current source and contacting an inside wall of a pipe of a given material to flow a current into the pipe from the alternating current source between the two electric connectors, wherein the pipe is located downhole in a formation; 
 a magnetic sensor positioned between the two electric connectors and operable to receive a magnetic field in response to flowing the current while the magnetic sensor scans over the inside wall of the pipe, wherein the scanning includes moving the magnetic sensor azimuthally around the inside wall of the pipe and longitudinally along the inside wall of the pipe; 
 a processing unit operable to process the magnetic field to detect that a defect is located at a given azimuth and a given longitudinal position of the pipe and has a defect thickness, wherein the detection is based on: (i) a maximum strength of the magnetic field in a transverse direction to a longitudinal axis direction of the pipe; (ii) a maximum strength of the magnetic field in the longitudinal axis direction of the pipe; and (iii) calibration data for the given type material which correlates the maximum strength of the magnetic field in the transverse and longitudinal axis direction to the defect thickness. 
 
     
     
       2. The apparatus of  claim 1 , wherein the two electric connectors maintain contact along an inside wall of the pipe as the two electric connectors slide or spiral along the inside wall. 
     
     
       3. The apparatus of  claim 1 , wherein the two electric connectors are brush type connectors. 
     
     
       4. The apparatus of  claim 1 , wherein the two electric connectors are bow-spring connectors. 
     
     
       5. The apparatus of  claim 1 , wherein the apparatus includes the processing unit operable to process the magnetic field and to generate a representation of an anomaly in the pipe. 
     
     
       6. The apparatus of  claim 5 , wherein the representation includes a representation of shape, size, or a combination of shape and size. 
     
     
       7. The apparatus of  claim 1 , wherein the magnetic sensor is a coil or a magnetometer. 
     
     
       8. The apparatus of  claim 1 , wherein the magnetic sensor is operable to rotate and detect azimuth angles indicating edges of a detected anomaly. 
     
     
       9. The apparatus of  claim 1 , wherein the two electric connectors contacting the inside wall of the pipe are coupled to respective conductors, wherein the respective conductors are insulated from each other by an insulator and coupled to the alternating current source, wherein the insulator and respective conductors are linearly arranged to span in between the two electric connectors, and wherein the respective conductors comprise a metal tubular. 
     
     
       10. The apparatus of  claim 1 , further comprising a drill collar of a drill string and a tool attached to the drill collar, wherein the two electrical connectors are coupled to the drill collar of the drill string to flow the current around a circumference of the wall of the pipe, wherein the tool includes the magnetic sensor. 
     
     
       11. The apparatus of  claim 1 , further comprising a motor that rotates one or more of the magnetic sensor and the two electric connectors inside the pipe to flow the current around a circumference of the wall of the pipe. 
     
     
       12. A method comprising:
 generating an alternating current in a wall of a pipe of a given material between two connectors contacting an inside of the wall, the two connectors coupled to a current source, wherein the pipe is located downhole in a formation; 
 moving the two connectors along the inside of the wall; and 
 determining that an anomaly exists in the pipe as the two connectors move along the inside of the wall by detecting a magnetic field in a magnetic sensor when scanning over the anomaly, the magnetic field indicative of the anomaly, wherein the scanning includes moving the magnetic sensor azimuthally around the inside wall of the pipe and longitudinally along the inside wall of the pipe; 
 wherein determining the anomaly comprises detecting that a defect is located at a given azimuth and a given longitudinal position of the pipe and has a defect thickness, wherein the detection is based on: (i) a maximum strength of the magnetic field in a transverse direction to a longitudinal axis direction of the pipe; (ii) a maximum strength of the magnetic field in the longitudinal axis direction of the pipe; and (iii) calibration data for the given type material which correlates the maximum strength of the magnetic field in the transverse and longitudinal axis direction to the defect thickness. 
 
     
     
       13. The method of  claim 12 , wherein the two connectors maintain contact along the inside of the wall of the pipe as the two connectors slide or spiral along the inside of the wall. 
     
     
       14. The method of  claim 12 , wherein the two connectors are brush type connectors. 
     
     
       15. The method of  claim 12 , wherein the two connectors are bow-spring connectors. 
     
     
       16. The method of  claim 12 , wherein the method includes processing a signal from the detected magnetic field, generating a representation of the anomaly in shape, size, or a combination of shape and size. 
     
     
       17. The method of  claim 12 , wherein the method includes rotating the magnetic sensor around the inside of the pipe. 
     
     
       18. The method of  claim 12 , wherein the magnetic sensor is a coil or a magnetometer. 
     
     
       19. The method of  claim 12 , wherein the method includes, based on determining that the anomaly exists, rotating the magnetic sensor to detect azimuth angles indicating edges of the anomaly. 
     
     
       20. The method of  claim 12 , wherein the two electric connectors contacting the inside wall of the pipe are coupled to respective conductors, wherein the respective conductors are insulated from each other by an insulator and coupled to the alternating current source wherein the insulator and respective conductors are linearly arranged to span in between the two electric connectors, and wherein the respective conductors comprise a metal tubular. 
     
     
       21. The method of  claim 12 , wherein moving the two connectors and the magnetic sensor comprises rotating a drill collar of a drill string which is coupled to the two connectors contacting the inside of the pipe, wherein the rotation causes the two connectors to rotate along the inside of the wall of the pipe to flow the current around a circumference of the wall of the pipe, wherein a tool is attached to the drill collar and wherein the tool includes the magnetic sensor. 
     
     
       22. The method of  claim 12 , wherein a motor is coupled to the two connectors in the pipe; and wherein moving the two connectors comprises rotating the two connectors along the inside of the wall via the motor to flow the current around a circumference of the wall of the pipe. 
     
     
       23. A system comprising:
 a pipe of a given material, the pipe positioned downhole in a well of a subsurface formation; 
 a housing positioned inside the pipe, the housing comprising an alternating current source, two electric connectors coupled to the alternating current source; and a magnetic sensor positioned between the two electric connectors; and 
 machine-readable storage device having instructions stored thereon, which, when performed by a machine, cause the machine to perform operations, the instructions comprising instructions to: 
 move the two electric connectors along the inside of a wall of the pipe, wherein the two electric connectors are in substantially continuous contact with the inside surface of the wall; 
 generate alternating current in a portion of the wall between the two connectors; 
 collect data from the magnetic sensor in response to the generated alternating current, wherein the collecting includes moving the magnetic sensor azimuthally around the inside wall of the pipe and longitudinally along the inside wall of the pipe; and 
 determine, from the collected data, if an anomaly exists in the pipe as the two electric connectors move along the inside of the wall; 
 wherein determining if an anomaly exists comprises detecting if a defect is located at a given azimuth and a given longitudinal position of the pipe and has a defect thickness, wherein the detection is based on: (i) a maximum strength of the magnetic field in a transverse direction to a longitudinal axis direction of the pipe; (ii) a maximum strength of the magnetic field in the longitudinal axis direction of the pipe; and (iii) calibration data for the given type material which correlates the maximum strength of the magnetic field in the transverse and longitudinal axis direction to the defect thickness. 
 
     
     
       24. The system of  claim 23 , wherein the instructions include instructions to:
 process the collected data and to generate a representation of the anomaly in shape, size, or a combination of shape and size; and 
 display an image of the anomaly. 
 
     
     
       25. The system of  claim 23 , wherein the instructions include instructions to determine, from the collected data, a first azimuth angle and a second azimuth angle indicating edges of a detected anomaly. 
     
     
       26. The system of  claim 23 , wherein the two electric connectors contacting the inside wall of the pipe are coupled to respective conductors, wherein the respective conductors are insulated from each other by an insulator and coupled to the alternating current source, wherein the insulator and respective conductors are linearly arranged to span in between the two electric connectors, and wherein the respective conductors comprise a metal tubular.